Magnetic diagenesis, organic input, interstitial water chemistry, and paleomagnetic record of the carbonate sequence on the Ontong Java Plateau

Abstract

Shipboard paleomagnetic studies on Ocean Drilling Program Leg 130 were plagued by severe reduction in the remanence intensity, which affected sediments below a sharply defined onset at sub-bottom depths of 50 mbsf or less. This loss of intensity was accompanied by a reduction in magnetic stability and consequent loss of polarity and paleolatitude information. Viscous remanent magnetization and drilling-induced remanences contributed high-coercivity overprints, further obscuring the greatly diminished primary magnetization. The depth at which the reduction in intensity occurred correlates with the organic carbon content of the sediments, and a further relationship is present between intensity downhole and the level of sulfate reduction. This implies that loss of intensity is related to the microbial reduction of magnetite. Reduction of sulfate results in the generation of a magnetic iron sulfide, which appears to be the carrier of the high-coercivity overprints. -from Authors